The invention relates in general to motor drives and in particular to traction motors.
The present invention relates to a variable frequency current converter for energizing an alternating current machine (or motor) from a controllable direct current power supply in order to enable the said machine to function at a controllable speed and with a controllable torque.
When so energized at variable frequency and voltage the AC motor operates with characteristic which is nearly the same as of a DC machine, without the drawback of a commutator.
In French Pat. Nos. 2,161,162 dated Nov. 16, 1971, and 2,194,346 dated Sept. 25, 1972, both of Albert Wiart, are described adjustable speed induction motor drives involving a direct current power source and thyristor switches but requiring the use of current choppers.
The object of the present invention is to make the use of a chopper optional and to provide apparatus requiring fewer components, thus less costly.
It is known to use capacitors for storing the energy employed in the commutation circuits, but such capacitors must operate at a fixed voltage.
Another object of the invention is to enable the use of capacitors with a variable voltage across the terminals.